
The function \(F\)  is not submodular as shown in [1]}. The current tightest estimation of the lower weak-submodular ratio of \(F\)  is due to Harshaw et al. [2]}. They show that \(\gamma \ge (1 + \frac{s^2}{\sigma ^2}\lambda _{\max }(\mathbf {\Lambda }))^{-1}\) , where \(s = \max _{i \in [n]} \Vert \mathbf {x}_i\Vert \) . Here we give a bound on the upper weak-submodularity ratio \(\beta \) .
